Biodegradable polyester is a kind of macromolecule material using biological resources as raw materials. With respect to a petroleum-based polymer using petrochemical resources as raw materials, the biodegradable polyester can be degraded during a process of biological or biochemical effect or in a biological environment, being a very active degradable material in the present biodegradable plastic research and one of the best degradable materials in market application.
At present, biodegradable polyester film takes one of the most important application fields of biodegradable polyester, mainly including grocery bag, garbage bag, shopping bag, mulching film and the like. During blow molding process of the biodegradable polyester in preparing films, it frequently appears that the film is not lubricating enough to adhere to a roll or is too lubricating to roll up. Thus it results in poor bubble stability and a large range of film thickness during film blowing which severely affect a continuity of film blowing. In CN 101622311A, by adding 0.05-5 wt % of biodiesel into a biodegradable polyester mixture, a viscosity of the polyester mixture is decreased, to some extent leading to less adherence of film to the roll, which guarantees the continuity of film blowing. However, a decrease of the viscosity of the polyester mixture indicates that an addition of biodiesel damages performances of the polyester to some extent, resulting in an increased melting index and a decreased viscosity of the polyester mixture.
In addition, during blow molding process of the biodegradable polyester in preparing films, ink supply is required and thereby a desired label and a logo are printed on the film. However, during the printing process of biodegradable polyester film, the printing is frequently unreliable (i.e. ink does not fully adhere to the film or an adhesion strength is not enough) or the printing is excessive (i.e. too much ink adheres to the film resulting the unclear logo), which indicates poor printing performance of the film.
The present invention surprisingly finds by research that by adding a trace amount of tetrahydrofuran and cyclopentanone into the biodegradable polyester composition can prevent the ink from stripping off the film material during the printing process and prevent excessive ink from adhering to the film material, so that the film shows excellent printing performance. Moreover, it enables the biodegradable polyester to have obviously improved film blowing properties. When a velocity of film blowing is relatively high, it presents good bubble stability as well as a relatively small range of film thickness and guarantees the continuity of a film blowing production.